1. Field of the Invention
This invention relates to a copying apparatus, and more particularly to a copying apparatus having a variable copying magnification.
2. Description of the Prior Art
An example of a copying apparatus having a variable copying magnification is disclosed in U.S. Pat. No. 3,476,478. This apparatus has an auxiliary lens movable into and out of the image side optical path (or the object side optical path) of a main focusing lens. By the movement of such auxiliary lens into or out of said optical path, the focal length of the focusing lens device is changed for decrease or increase. Also, in this apparatus, the focusing lens device is movable as a whole on its optic axis by a distance corresponding to the amount of variation in the focal length, toward the object side, i.e. the original side, or toward the image side, i.e. the photosensitive medium side, whereby the original to be copied and the photosensitive medium may be brought into a new optically conjugate relationship. Since, in the apparatus of this U.S. Pat. No. 3,476,478, the focusing lens device must be moved back or forth along its optic axis as noted above when the copying magnification is to be changed, it is impossible to provide coincidence between the side edges of the image formed at various magnifications on the photosensitive medium. For example, if a life-size image (A-3) of an original of A-3 size and an A-4 size image of the original of the same size were successively formed on the photosensitive medium, the leading end edges of these images could be made coincident by suitably synchronizing the rotation of the photosensitive drum with the scanning time of the original, but their side edges would be separate from each other. This is inconvenient to the copying apparatus of the type in which the side edge of transfer paper, whatever size it may be, must be registered to a predetermined line on the photosensitive medium.
The apparatus disclosed in U.S. Pat. No. 3,614,222 or Japanese Open Patent Application No. 99335/1975 has a movable focusing lens and a movable mirror in the optical path between the focusing lens and the object to be copied. When the copying magnification is to be changed, the positions of the lens and the mirror are changed to vary the object side optical path length and the photosensitive medium side optical path length, whereby the object and the photosensitive medium may be brought into a new conjugate relationship. In that case, the focusing lens is designed to be moved in a direction intersecting the optic axis, thereby enabling the side edges of the images at various magnifications to be coincident with each other. However, the apparatus of U.S. Pat. No. 3,614,222 or Japanese Open Patent Application No. 99335/1975 employs a fixed focal length lens and applies such lens to any copying magnification. On the other hand, it is difficult to design a fixed focal length lens which will have a high performance for any copying magnification. In other words, it is difficult to design a fixed focal length lens such that the fixed focal length lens which displays the highest performance in forming an image at a certain magnification also displays the highest performance in forming images at the other magnifications. It is therefore difficult for the above-described apparatus to produce copy images of high quality.
Further, in any of the well-known apparatuses described above, the focusing lens system is designed to be moved and this necessitates the provision of precise means for moving and positioning the lens system.